1. Field of the Invention
This invention relates to substrate treating apparatus and methods for treating, with a treating solution, substrates such as semiconductor wafers, glass substrates for liquid crystal displays and glass substrates for photomasks (hereinafter simply called “substrates”).
2. Description of the Related Art
A conventional apparatus of the type noted above has a nitrogen gas source, a regulator, a supply pipe and a pressure detector (Japanese Unexamined Patent Publication No. 11-219931 (1999), (paragraphs “0040” to “0050” and FIG. 2), for example). This apparatus supplies nitrogen gas at a constant flow rate from the nitrogen gas source into a treating tank, with a detection end of the supply pipe disposed at a predetermined depth in the tank. The pressure detector detects a pressure of the nitrogen gas supplied into the treating tank. The pressure detected in this way is a pressure at the predetermined depth in the treating tank, and has a correlation with the specific gravity of a treating solution. The concentration of the treating solution is controlled based on the detected specific gravity, for example.
Specifically, the apparatus further includes a voltage converter for converting the pressure detected by the pressure detector into voltage. This voltage is applied to a controller for displaying its value and controlling the pressure.
The above conventional example has the following drawbacks.
With the conventional apparatus, the pressure detected is variable even with slight variations in the position of the detection end of the supply pipe. Thus, the pressure varies each time the height of the supply pipe is adjusted. The pressure is variable also among different apparatus of the same construction. The detected pressure serves only as a reference peculiar to the apparatus concerned. This pressure cannot be used for comparison with other apparatus of the same construction. In addition, the detected pressure, i.e. the meaning of voltage, is unintelligible to the user. Further, when adjusting treating conditions of the apparatus, the adjustment must be carried out in a way suited for each individual apparatus, resulting in increased man-hours.